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CARDIOVASCULAR
SYSTEM
• The entire cardiovascular system – the
heart, blood vessels, and blood cells –
originate from the Mesodermal germ
layer.
• The vascular system of the human embryo
appears in the middle of the 3rd week.
Angiogenic Cell Clusters
• The origins of the heart tube are clusters
of Angiogenic cells which are located in
the cardiogenic plate. The cardiogenic
plate, which is derived from
splanchnopleuric mesoderm, is located
cranial to the neural plate.
Endocardial Tubes
• These Angiogenic cell clusters coalesce to
form right and left endocardial tubes.
• Each tube is continuous cranially with a
dorsal aorta, its outflow tract, and caudally
with a vitteloumbilical vein, its inflow tract.
• The lateral and cranial folding of the
embryo forces the tubes into the thoracic
cavity. As a result, these tubes come to lie
closer to each other and begin to fuse in a
cranial to caudal direction.
• At approximately day 21 they are
completely fused.
Heart Tube
• The newly formed heart tube bulges into the
pericardial cavity and is attached to the dorsal
wall by a fold of tissue, the dorsal mesocardium.
This is a derivative of foregut splanchnoplueric
mesoderm. Eventually this will rupture leaving
the heart tube suspended in the pericardial
cavity anchored cranially by the dorsal aortae
and caudally by the vitteloumbilical veins.
• As it bulges into the cavity it becomes invested
in a layer of myocardium. A layer of acellular
matrix, the cardiac jelly, separates the
myocardium and the endothelial heart tube.
• The newly formed heart tube may be divided into
different regions. Starting caudally:
• Sinus venosus - consisting of right and left horns.
• Paired primitive atria. These structures will later fuse
together to form common atrium.
• Atrioventricular sulcus divides the atria and the
primitive ventricle.
• Primitive ventricle expands to become the left ventricle.
• Interventricular sulcus divides the primitive ventricle
and the bulbus cordis
• Bulbus cordis which may be divided as follows:
• Bulbus cordis - the proximal portion forms the right
ventricle
• Conus cordis
• Truncus arteriosus
• Aortic sac
–By the time the heart tube has formed
the bulboventricular loop, the two
primitive right and left atria have fused to
form a common atrium.
–Note that it now lies cranial to the
primitive ventricle and dorsal to the
bulbus cordis.
–The truncus arteriosus lies on the roof of
the common atrium causing a
depression and indicates where
septation of the atrium will occur.
• The partitioning of the atrium begins with
the appearance of septum primum at
about the 28th day.
• This is a crest of tissue that grows from
the dorsal wall of the atrium towards the
endocardial cushions - - the ostium
(opening) formed by the free edge of
septum primum is the ostium primum.
• Before the septum primum fuses with the
endocardial cushions, perforations appear
in the upper portion of the septum primum.
• These perforations will coalesce to form
the ostium secundum
• Septum secundum does not fuse with the
endocardial cushions.
• Its free edge forms the foramen ovale.
• The left venous valve and the septum
spurium, located on the dorsal wall of the
right atrium, fuse with the septum
secundum as it grows.
• At the end of the seventh week the human heart has
reached its final stage of development.
• Because the fetus does not use its lungs, most of the
blood is diverted to the systemic circulation. This is
accomplished by a right to left shunting of blood that
occurs between the two atria.
• The foramen ovale and the septum primum control this
right and left communication.
• The septum primum acts as a valve over the foramen
ovale.
• At birth the child will use its lungs for the first time and
consequently more blood will flow into the pulmonary
circulation.
• The pressure increase in the left atrium (where the
pulmonary veins empty) will force septum primum to be
pushed up against septum secundum.
• Shortly thereafter the two septa fuse to form a common
atrial septum.
Sinus Venosus
Each horn receives venous blood from three
vessels:
1. Vitelline vein
2. Umbilical vein
3. Common cardinal vein
The fate of each structure is as follows:
• the right sinus horn becomes enlarged
• the right common cardinal vein ( along
with some proximal portion of right ant.
Cardinal vein) becomes the superior vena
cava.
• the right Vitelline vein becomes the inferior
vena cava
• the right umbilical vein is obliterated
• Conversely, the left vein counterparts are
obliterated and the left sinus horn
diminishes in size and forms the coronary
sinus and the oblique vein of the left
atrium.
Pulmonary veins
• Development of the left atrium occurs
concurrently with that of the right atrium.
• During the early part of the fourth week an
outgrowth of the pulmonary veins appear
from the left atrium.
• This "sprout" will bifurcate until there are
four veins.
• These vessels will then grow towards the
lung buds.
Ventricles
• Primitive ventricle expands to become
the left ventricle.
• Externally the interventricular sulcus
separates the right and left ventricles and
internally they are separated by the
bulboventricular tissue
• Bulbus cordis - the proximal portion
forms the right ventricle
• Both ventricles will
continue to expand
until the late 7th/early
8th week. The growth
of the ventricles is
due to the centrifugal
growth of the
myocardium and the
diverticulation of the
internal walls
• The muscular interventricular septum
forms as a result of the expanding
ventricles.
• The walls of the right and left ventricles
grow in opposition to each other to form
the muscular septum.
• Thus, the septum will cease to grow when
the ventricular walls are no longer
expanding.
Atrioventricular canals
• Swellings of mesenchymal tissue, the
endocardial cushions, appear on the
borders of the atrioventricular canal
• There are four cushions: inferior and
superior (ventral and dorsal), left and right.
These swellings give the atrioventricular
canal a "dog's bone" shape.
• At approximately day 42 the superior and
inferior cushions fuse forming a right and a
left atrioventricular canal.
• Now, the left atrium communicates with
the left ventricle and the right atrium
communicates with the right ventricle
• The fused endocardial cushions are also
responsible for the closure of the ostium
primum by fusing with the free edge of the
septum primum
Partitioning of the Outflow Tract
• The final morphological change in the
heart is the partitioning of the outflow tract
- -the truncus arteriosus and the conus
cordis - - into the aorta and the pulmonary
trunk.
• This is accomplished by the development
of a septum that forms in the outflow tract
and the emergence of the two great
vessels.
• The septum forms
from two pairs of
swellings which grow
from the walls of the
outflow tract. These
are the truncus
swellings and the
conus swellings
Truncal swellings
• Right superior which grows distally and to
the left. Left inferior which grows distally
and to the right. Both develop at the
proximal part of the truncus and proceed
to grow in two directions; 1) distally
towards the aortic sac and 2) into the
lumen of the outflow tract where they will
eventually fuse together
Conus swellings
• Right dorsal which is continuous with the
right superior Left ventral which is
continuous with the left inferior like the
truncal swellings, the conal swellings grow
distally and towards each other, however
they appear after the truncal swellings.
Arterial system (Aortic arches)
• Branchial arches has own artery. These
arteries are known as Aortic arches.
• Aortic arteries arise from aortic sac, the
most distal part of the truncus arteriosus.
• Total six pairs of arteries arise
corresponding to arches.
• Aortic sac forms right and left horns—
brachiocephalic artery.
• 1st aortic arch (part) - maxillary artery.
• 2nd aortic arch some part forms hyoid and
stapedial arteries.
• Rest of 1st and 2nd arch disappears.
• 3rd aortic arch- common carotid artery and first
part of the internal carotid artery and external
carotid artery.
• 4th aortic arch
Left side—arch of aorta.
Right side – proximal segment of the right
subclavian artery.
• Fifth aortic arch is transient and is never
well developed.
• 6th aortic arch (pulmonary arch)
Right side – proximal part forms proximal
segment of the right pulmonary artery.
Left side -- the distal part persists during
intra uterine life as the ductus arteriosus.
Vitelline arteries
• Initially a number of paired vessels
supplying the yolk sac, gradually fuse to
form the arteries located in the dorsal
mesentery of the gut.
• They are represented by celiac, superior
mesenteric and inferior mesenteric
arteries.
Umbilical arteries
• The proximal portion after birth is
represented as internal iliac and superior
vesical arteries.
• While the distal parts are obliterated to
form the medial umbilical ligaments.
Venous system
Mainly 3 pairs of major veins formed in 5th week.
1.Vitelline or Omphalomesenteric veins carrying
blood from the yolk sac to the sinus venosus.
2. Umbilical veins—originating in the chorionic villi
and carrying oxygenated blood to the embryo.
3. Cardinal veins- draining the body of the embryo
proper.
• The anastomatic network of Vitelline veins
around the duodenum develops into single
vessel (vein) - PORTAL VEIN.
Umbilical veins
• With the increase of the placental circulation, a
direct communication is formed between the left
umbilical vein and the right hepatocardiac
channel , by DUCTUS VENOSUS.
• After birth left umbilical vein and ductus venosus
are obliterated and form the ligamentum teres
hepatis and ligamentum venosum respectively.
Cardinal veins
• Anterior cardinal veins- drain cephalic part
of the embryo.
• Posterior cardinal vein- drain remaining
part of the body of the embryo.
• Anterior and posterior veins join to form
short common cardinal veins.
Contd.. Cardinal veins
• Other than this
• Subcardinal veins- drain kidneys.
• Sacrocardinal veins- drain lower
extremities.
• Supracradinal veins- drain body wall.
• Anastomosis between the anterior cardinal
veins develops into left brachiocephalic
vein.
Contd.. Cardinal veins
• Superior vena cava is formed by the right
common cardinal vein and the proximal portion
of the right anterior cardinal vein.
• Anastomosis between the Subcardinal veins
forms the left renal vein.
• Anastomosis between the Sacrocardinal veins
forms the left common iliac vein.
Abnormalities of Great Arteries
• PATENT DUCTUS ARTERIOSUS- under
normal condition the ductus arteriosus is
functionally closed through contraction of
its muscular wall shortly after birth.
• Patent ductus arteriosus is one of the most
frequently seen abnormalities of the great
vessels.
Abnormalities of Great Arteries
• Coarctation of the Aorta
In this condition the aortic lumen below the
origin of the left subclavian artery is
significantly narrowed.
The umbilical vein enters the body through
the umbilical ring and travels along the
anterior abdominal wall to the liver.
• About 1/2 the blood it carries passes into
the liver.
• The other 1/2 of the blood enters a vessel
called the ductus venosus which
bypasses the liver.
– The ductus venosus travels a short distance
and joins the inferior vena cava.
– There, the oxygenated blood from the
placenta is mixed with the
deoxygenated blood from the lower
parts of the body.
This mixture continues through the
vena cava to the right atrium
In the adult heart, blood flows from the
right atrium to the right ventricle then
through the pulmonary arteries to the
lungs.
In the fetus however, the lungs are
nonfunctional and the blood largely
bypasses them.
• As the blood from the inferior vena cava
enters the right atrium, a large proportion
of it is shunted directly into the left atrium
through an opening called the foramen
ovale.
• Septum primum is located on the left side
of the atrial septum overlies the foramen
ovale and helps prevent blood from
moving in the reverse direction. Thus,
acting as a valve.
The rest of the fetal blood entering the
right atrium, including a large proportion
of the deoxygenated blood entering from
the superior vena cava passes into the
right ventricle and out through the
pulmonary trunk.
 Only a small volume of blood enters
the pulmonary circuit, because the
lungs are collapsed, and their blood
vessels have a high resistance to flow.
 Enough blood reaches the lung tissue
to sustain them.
Most of the blood in the pulmonary
trunk bypasses the lungs by entering a
fetal vessel called the ductus
arteriosus which connects the
pulmonary trunk to the descending
portion of the aortic arch.
• As a result of this connection, the
blood with a relatively low O2
concentration which is returning to the
heart through the superior vena
cava, bypasses the lungs.
• At the same time, the blood is
prevented from entering the portion of
the aorta that provides branches
leading to the brain.
• The more highly oxygenated blood that
enters the left atrium through the
foramen ovale is mixed with a small
amount of deoxygenated blood returning
from the pulmonary veins.
• This mixture moves into the left ventricle
and is pumped into the aorta.
• Some of it reaches the myocardium
through the coronary arteries and some
reaches the brain through the carotid
arteries.
• The blood carried by the descending
aorta is partially oxygenated and partially
deoxygenated.
• Some of it is carries into the branches of
the aorta that lead to various parts of the
lower regions of the body.
• The rest passes into the umbilical
arteries, which branch from the internal
iliac arteries and lead to the placenta.
• There the blood is reoxygenated.
Lymphatic system
• Lymphatic system begins its development after
CVS.
• The exact origin is not clear but may be from
mesenchyme.
• As a result 6 primary lymph sacs are formed.
• Two jugular, two iliac, one retroperitoneal and
one cisterna chyli.
• Numerous channels contact the sacs with each
other and also drain lymph from the entire body
of the embryo proper.
• The two main channels the right and left thoracic
ducts join the jugular sacs with the cisternachyli,
and forma an Anastomosis.
• Thoracic duct develops from dorsal portion of
right thoracic duct and Anastomosis and cranial
portion of left thoracic duct.
• Right lymphatic duct is derived from the cranial
portion of the right thoracic duct.
• Both ducts maintain their original connection
with the venous system and empty in to the
junction of the internal jugular and subclavian
veins.
CLASSIFICATION OF CHD
Left to right shunt
•
VSD, ASD, PDA, PTA
Right to left shunt
•
Tetralogy of Fallot
No shunt
•
Transposition of great vessels
• Stenosis, coarctation
• Valvular anomalies
Atrial Septal Defect
• There are two types of ASD:
• Primum type involves the endocardial
cushions.
• Secundum type involves septum primum
or septum secundum
ATRIAL SEPTAL DEFECT
Ostium secundum type (90%)
Ostium primum type
Sinus venosus defect
Persistent common
atrioventricular canal
DD: patent foramen ovale (25%
adults)
Secundum Type ASD
• This type involves septum primum and/or
septum secundum. In both cases the
result is a patent foramen ovale.
Persistent Atrioventricular Canal
• The persistent atrioventricular canal
results from the failure of the superior and
inferior cushions to fuse
• Thus there is a single atrioventricular
canal in which all four chambers may
freely communicate
Ventricular Septal Defect
• The ventricular septal defect is the most
common of all congenital heart anomalies.
It may be caused by any of the four
malformations:
(1) Deficient development of the proximal
conus swellings.
(2) Failure of the muscular portion of the
interventricular septum to fuse with the
free edge of the conus septum.
(Membranous VSD)
(3) Failure of the endocardial cushions to
fuse.
(4) Excessive diverticulation of the muscular
septum- perforations in the muscular
interventricular septum. (Muscular VSD)
• In the case of a VSD there is a massive
left to right shunting of blood and
pulmonary hypertension.
• The absence of the interventricular septum
sometimes results in a Common Ventricle
Transposition of the Great
Vessels
• Transposition is a condition in which the
aorta arises from the right ventricle and
the pulmonary trunk from the left ventricle.
• This anomally is due to the failure of the
truncoconal swellings to grow in the
normal spiral direction
• Mostly in Transposition ,there is also a
ventricular septal defect and a patent
ductus arteriosus.
• These secondary defects make life
possible as they provide a way for
oxygenated blood to reach the entire body
Persistent Truncus Arteriosus
• Mostly persistent truncus arteriosus results
when the truncoconal swellings fail to grow
• Again there also there is mixture of the
blood.
Tetralogy of Fallot
• This condition commonly and mainly
results from a single error: the conus
septum develops too far anteriorly giving
rise to two unequally proportioned vessels- a large aorta and a smaller stenotic
pulmonary trunk.
The four main characteristics of Tetralogy of Fallot
are:
(1) Pulmonary stenosis
(2) Ventricular septal defect (VSD) of the
membranous portion
(3) Overriding aorta (the aorta straddles the VSD)
(4) Right ventricular hypertrophy due to the
shunting of blood from left to right. (The pressure
in the right ventricle is increased causing the
walls of the right ventricle to expand.)
Dextrocardia
• Mostly seen variety is due to
• Dextrocardia is an anomaly in which the
primitive heart tube folds to the left in a
mirror image of a normal bulboventricular
loop.
• This usually occurs when all the organ
systems are reversed, a condition called
situs inversus.